This project involved the same seven communities in Illinois that had been previously surveyed by the NIDR in April 1980. The communities were grouped according to the relation of their water fluoride concentration for the area (1, 2, 3, or 4-times optimal). Study participants consisted of children in two age groups, 8-to- 10 and 13-to-15 years of age. The 8-to-10 year age group comprised children who received parental consent to participate and whose histories indicated that they had resided continuously since birth in their respective communities. The 13-to-15 year old group comprised only those children who were examined as 8-to-10 year olds in 1980. Examinations for the survey were conducted in April 1985. Dental caries was assessed with the DMFS index and fluorosis was measured with the Tooth Surface Index of Fluorosis, an index developed by NIDR for the 1980 survey. These indices were applied in both age groups by the same examiners who had used them in 1980. A new examiner assessed the prevalence of gingivitis and calculus in the entire dentition in the 13-to-15 year age group. A report presenting findings on dental caries and fluorosis has been published.